homelab-notes/proxmox1/gpu-passthrough-notes.md

GPU Passthrough (VFIO) Notes

Host/guest checklist for GPU passthrough (or virtual GPU) when building Debian VMs in Proxmox / virt-manager style setups.

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Host: Pick GPU and enable passthrough

List GPUs on the host:

lspci | egrep -i 'vga|3d|display'

Note the PCI ID of the card you want to pass, e.g. 0000:01:00.0.

On the host, enable IOMMU and passthrough (Proxmox/virt-manager style):

• Add appropriate kernel params (example Intel):

intel_iommu=on iommu=pt

• Reboot and verify:

dmesg | egrep -i 'iommu|dmar'

Bind the GPU to vfio (or equivalent passthrough driver) on the host so the VM can own it exclusively.

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Host: Create the VM with a VGA/GPU device

Create a new VM (Proxmox or virt-manager):

• Firmware: UEFI/OVMF if possible
• Machine type: Q35/modern
• CPU: host-passthrough (or similar)

Add GPU to the VM:

• Add PCI device: select your GPU (and its audio function if present)
• For a purely virtual GPU instead (no passthrough), pick Virtio GPU or QXL as the display adapter

Add display channel:

• If you want a normal graphical console, use SPICE (virt-manager) or Proxmox’s standard console display
• Add a Channel (spice) device for clipboard/resize when using SPICE

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Guest: Verify what GPU the VM sees

Inside the guest OS (your Debian VM):

lspci | egrep -i 'vga|3d|display'
lsmod | egrep 'nvidia|amdgpu|radeon|virtio_gpu'

Interpretation:

• NVIDIA Corporation ... → real NVIDIA passthrough
• Advanced Micro Devices, Inc. [AMD/ATI] ... → AMD passthrough
• Red Hat, Inc. Virtio GPU or QXL → virtual GPU only

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Guest: Install and test drivers

If NVIDIA passthrough

Install driver and tools:

sudo apt update
sudo apt install nvidia-driver-535 nvidia-smi

(Adjust version to what Debian suggests.)

Test:

nvidia-smi
watch -n 1 nvidia-smi

The watch line must be watch -n 1 nvidia-smi.

Quick 3D check:

sudo apt install mesa-utils
glxgears

GPU utilization should rise in nvidia-smi while glxgears runs.

If AMD passthrough

Inspect and ensure amdgpu is used:

sudo lshw -c video
lsmod | grep amdgpu

Install tools:

sudo apt install mesa-utils
# optionally:
sudo apt install amdgpu-tools  # or ROCm SMI tools if available

Monitor:

watch -n 1 sudo amd-smi

(Or the ROCm SMI CLI in your distro.)

If only Virtio/QXL is present

• You have a virtual GPU, not the physical one.
• You can still use glxgears and basic acceleration, but host GPU usage is not controlled directly from inside this VM.
• To use the physical card, change the VM to PCI passthrough as above.

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Guest: Console and SPICE/GUI behavior

• With SPICE display and the spice channel present, dynamic resolution and clipboard should work once guest tools are installed.
• If a graphical display manager (e.g. LightDM) misbehaves, you can force a TTY-only boot:

sudo systemctl set-default multi-user.target
sudo systemctl disable --now lightdm.service

This gives you a reliable text console, and you can work purely over SSH for GPU workloads.